1. Field of the Invention
The present invention relates to a medical imaging system, particularly to a medical imaging system including an X-ray Talbot imaging apparatus.
2. Description of Related Art
In general, simple X-ray images (i.e., absorption images) of patient's joint cartilage cannot be captured with traditional silver halide films. Magnetic resonance imaging (MRI), which can image joint cartilage, produces low-definition images and cannot always measure quantitative feature values, such as the levels of defect, damage, and abrasion of cartilage due to arthritis or arthrorheumatism. In a conventional diagnosis of knee arthrorheumatism, a doctor estimates the thickness, abrasion or the like of the cartilage that is not visualized in a simple X-ray image of patient's knee, from the distance of a gap in the knee joint.
An X-ray imaging apparatus is known that includes a Talbot interferometer by the Talbot effect, which achieves imaging by sensing the phase shifts in X-rays passing through an object. An X-ray imaging apparatus is also known that includes a Talbot-Lau interferometer which is an application of the Talbot interferometer (see U.S. Pat. No. 5,812,629, Japanese Unexamined Patent Application Publication No. 2008-200359, and WO2011/033798, for example). In this specification, an X-ray imaging apparatus including a Talbot interferometer or a Talbot-Lau interferometer is called “X-ray Talbot imaging apparatus”. In specific, an X-ray Talbot imaging apparatus may be not only an X-ray imaging apparatus including a Talbot interferometer but also an X-ray imaging apparatus including a Talbot-Lau interferometer.
An X-ray Talbot imaging apparatus produces one or more moire images, which can be reconstructed into at least three types of images by analyzing multiple moire images taken by a scheme using the principle of fringe scanning or by analyzing a single moire image by the Fourier transform. The three types of images consist of an absorption image (the same as an X-ray absorption image explained above) reflecting the contrast produced by X-ray absorption, a differential phase image reflecting the contrast based on phase information, and a small-angle scattering image reflecting the contrast produced by small-angle scattering.
The inventors have applied an X-ray Talbot imaging apparatus to imaging of joint cartilage and found that an X-ray Talbot imaging apparatus can produce at least differential phase images of joint cartilage in an incised joint, as disclosed in Nagashima Masabumi and seven others. “Optimization of Joint and Cartilage: Diagnostic Potential of Differential Interferential Contrast X-ray Imaging”. Proceedings of the 14th Japanese Research Society of Clinical Anatomy, Sep. 11, 2010. Japanese Research Society of Clinical Anatomy, February 2011, No. 11, pp. 56-57, http://www.jrsca.jp/contents/records/ (accessed on Nov. 21, 2013). The inventors have also found that reconstructing a captured moire image of a joint in a living body instead of an incised joint the image also produces at least a differential phase image of joint cartilage.
With a conventional X-ray imaging apparatus, which cannot visualize cartilage in a captured image of patient's joint as described above, the doctor should estimate the thickness, abrasion or the like of the cartilage from the distance of a gap between two bones forming, for example, a knee joint. Consequently, the thickness or the like of cartilage cannot be quantitatively measured. Since the estimation depends on the experience or techniques of the radiologist, the estimated thickness or the like of cartilage may vary depending on the radiologist, inhibiting the consistency of the estimations.
If patient's joint cartilage is visualized in a differential phase image reconstructed from moire images taken with an X-ray Talbot imaging apparatus, the thickness or the like of the cartilage can be quantitatively measured in reference to the image of the cartilage. Referring to the differential phase image of the cartilage, the thickness or the like of the cartilage can be consistently measured independently of the experience or techniques of the radiologist. Thus, a measure is required which allows a medical imaging system including an X-ray Talbot imaging apparatus to quantitatively and consistently measure the thickness or the like of patient's joint cartilage from a differential phase image reconstructed from moire images taken with the X-ray Talbot imaging apparatus.